1. Field of the Invention
This invention relates to multilayer plastic structures, for example, film and sheet structures suitable for forming articles, for example, containers. More particularly, this invention is directed to multilayer asymmetric foilless plastic film and sheet structures suitable for forming containers, for example, collapsible dispensing containers, e.g., tubes, for packaging food, dentifrice, cosmetic, industrial, home-use and other products. The invention is also directed to such containers and methods of making the structures.
2. Description of Related Art
Collapsible dispensing containers, such as tubes for packaging food products, dentifrices and cosmetics have been in use for many years. Historically, the tubular bodies of such tubes have been made of a single layer of metal or plastic, multiple layers comprised of plastic, metal foil and/or paper, and, more recently, multiple layers of only plastics. The all-metal tube bodies are excellent barriers to oxygen, and they deform readily and have excellent product dispense properties, including excellent deadfold properties. That is, they deform, crease or fold easily and retain their deformed, creased or folded shape. However, they dent easily and they tend to crack with a moderate number of repeated flexures. Multilayer tubular bodies which include plastic layers and a layer of foil are advantageous in that the plastic layers are aesthetically pleasant, dent less and provide a smooth feel and a better print surface. The plastic layers protect the foil layer, reduce its tendency to crack on flexing, and isolate it from the packaged product. The metal foil layer is an excellent barrier to oxygen and it can provide good deadfold properties when employed in certain thicknesses and plastic layer configurations. The plastic layers generally have memory such that when they are deformed to dispense product, they tend to return to their original undeformed shape.
Commercial multilayer foil-containing film or sheet structures and collapsible dispensing tubes made therefrom for packaging dentifrice generally have had seven or more, typically eight or more layers. These tubes generally exhibit good product dispense properties. They tend to have good deadfold properties. Container bodies that do not have good deadfold properties tend to spring back after squeezing and dispensing product and tend to simultaneously suck air and product back into the container or container neck through its dispense orifice. This phenomena is referred to as xe2x80x9csuckbackxe2x80x9d. The air tends to oxidize or thicken the product and is expelled initially on the next squeezing or compression of the container. This can create undesirable audible effects, splattering, and reduced volume and non-uniform product dispensing. Thus, good product dispense properties, including good deadfold properties in multilayer collapsible dispensing tubes are desirable to reduce or eliminate suckback. They are also desirable to move product to and retain it in as-squeezed locations close to the tube""s dispense orifice, and to facilitate and effectuate more rapid and more uniform and complete product dispensing.
Although foil-containing collapsible dispensing tubes have been suitable for many years, recently, in an effort to simplify and reduce the cost of producing multilayer collapsible dispensing tubes, the tube making industry has developed multilayer plastic, i.e., foilless, sheet structures and collapsible dispensing tubes to replace multilayer foil-containing structures and tubes. The production of foil-layer-containing sheet structures is involved because it requires lamination, for example, extrusion lamination and/or coating processes, while foilless plastic structures can be produced by a one step coextrusion process. Also, expensive metal foils can be replaced with plastic materials that provide sufficient barrier properties. Further, plastic structures hold the promise of using of fewer layers.
Yet, coextruded plastic multilayer sheet and collapsible dispensing tubes made therefrom have had their drawbacks. One is that the coextruded plastic sheet has not had sufficient deadfold properties, and hence tubes made therefrom have not had sufficient product dispense properties as compared to those of multilayer foil-containing sheet and tubes. Another is that multilayer plastic sheet, when it is asymmetric has not been formable into cylindrical tubular bodies on commercial tube making equipment because the sheet curls excessively. One reason is that the most commonly-used and effective plastic barrier layer replacement material for metal foil, ethylene vinyl alcohol copolymer (xe2x80x9cEVOHxe2x80x9d), tends to be stiff and appears to have properties that cause or contribute to excessive curling of asymmetric coextruded multilayer plastic sheet structures. Heretofore, to avoid excessive curling, the EVOH layer or layers has been symmetrically positioned, that is balanced, in the multilayer plastic sheet structure. This means that, for example, the EVOH layer has been positioned as the central layer of the structure, or, if it is not the central layer, it has been balanced by the use of another EVOH layer on the opposite side of the structure. Thus, in the commercial nine-layer coextruded multilayer plastic sheet having polyethylene (outer) /adhesive /EVOH/ adhesive/bulk/adhesive/EVOH/adhesive/polyethylene (inner) layers, the bulk layer is the central layer and the EVOH layers are similarly positioned to either side of the bulk layer. Thus, the 9-layer sheet structure is symmetric. It does not exhibit a curling problem. Curling refers to the fact that the multilayer coextruded film and sheet (herein often merely referred to as xe2x80x9csheetxe2x80x9d) does not lay flat on a flat surface but curls upward from the surface. This makes the sheet difficult to handle. Curling persists even after the sheet has been wound on a roll during a typical storage period of several months and then unwound and used to make tubes. In commercially forming tubes, normal coextruded sheet has its inner surface-layer facing up and is wrapped about a cylindrical mandrel, and edges or edge portions of the sheet are joined together to form a cylindrical tubular body. However, asymmetric multilayer plastic sheet whose EVOH layer is not the central layer and is not otherwise balanced out positionally, tends to curl excessively and particularly downwardly in the direction of the outer surface layer (opposite to the direction desired). Hence, using commercial tube making equipment, the curved sheet is difficult to wrap around the mandrel and shape into a tubular body. If such sheets that exhibit excessive curling are formed into tubular bodies, the bodies are problematical because they tend to be oval rather than annular in cross sectional configuration. Consequently, they are difficult to load on cylindrical mandrels of tube heading machines that add or join a tube head to the tubular body. Even if successfully headed, such tube bodies have oval open ends that are difficult to fill with product because the nozzles or product filling lines typically are cylindrical and do not readily align with or fit into the oval open ends of the tube bodies. Thus, the nozzles sometimes crush the open ends of the tube bodies and/or deposit product on the outside surfaces of the tube bodies and on the filling equipment. These occurrences can cause filling line shut downs.
In view of the foregoing, it is an object of this invention to provide improved multilayer plastic structures, for example, film and sheet structures, that are suitable for producing improved collapsible dispensing containers for packaging food, dentifrice, cosmetic, industrial, home-use and other products.
It is another object of this invention to provide improved multilayer plastic film and sheet structures and collapsible dispensing containers made therefrom that are less expensive to produce than multilayer metal foil layer-containing structures and containers.
Another object of this invention is to provide aforementioned improved containers that have improved product dispense properties as compared to the product dispense properties of multilayer foil layer-containing collapsible dispense containers.
Another object of this invention is to provide aforementioned multilayer plastic film and sheet structures that have improved deadfold crease retention properties, and can, for example, be used to produce collapsible dispensing containers having such properties.
Another object of this invention is to provide the aforementioned containers with improved deadfold properties and hence acceptable levels of product suckback.
Another object of this invention is to provide asymmetric ethylene vinyl alcohol layer-containing multilayer plastic film and sheet structures that have acceptable levels of curling.
Another object of this invention is to provide six-layer asymmetric ethylene vinyl alcohol layer-containing plastic film and sheet structures that have acceptable levels of curling.
Yet another object of this invention is to provide aforementioned asymmetric film and sheet structures that can be formed into cylindrical tube bodies.
Yet another object of the invention is to provide aforementioned film and sheet structures and tubular bodies made therefrom whose surfaces are free of voids.
Still another object of this invention is to provide collapsible dispensing containers, i.e., tubes, whose body walls have improved column strength.
Still another object of this invention is to provide methods of producing the aforementioned improved film or sheet structures.
This invention is directed to a coextruded asymmetric multilayer plastic structure whose layers consist of a barrier layer comprised of an ethylene vinyl alcohol copolymer, an adhesive layer on each surface of the barrier layer, inner and outer surface layers, and a bulk layer positioned between one of the surface layers, preferably directly between the outer surface layer and an adjacent one of the adhesive layers, the bulk layer being comprised of a thermoplastic polymer and calcium carbonate in an amount sufficient that the multilayer structure has an acceptable level of curling. The bulk layer can include from about 30 to about 75 percent by weight calcium carbonate based on the weight of said bulk layer, higher loadings within the range, being preferred.
The structure can be a sheet having a thickness of 10 mils or more, or a film having a thickness of less than 10 mils. The structure can be a tubular body that has a longitudinal axis, a seam parallel to the axis and a cylindrical shape when viewed in cross section taken orthogonally across the axis. The tubular body can have two opposed open ends, one joined to a head to form a collapsible dispensing tube and the other having a cylindrical shape when viewed in cross section taken orthogonally across the axis. The thermoplastic polymer of the bulk layer preferably is comprised of polyolefins. For example, the bulk layer can be comprised of from about 10 to about 60 wt. % high density polyethylene, from about 10 to about 25 wt. % linear low density polyethylene, from about 3 to about 6 wt. % low density polyethylene, and from about 5 to about 25 wt. % of reground scrap from the structure.
The bulk layer can be comprised of about 52.5 wt. % calcium carbonate, about 17.5 wt. % linear low density polyethylene, about 20 wt. % high density polyethylene and about 3 wt. % low density polyethylene; or about 52.5 wt. % calcium carbonate, about 17.5 wt. % linear low density polyethylene, about 10 wt. % high density polyethylene, about 10 wt. % of reground scrap from the structure and about 3 wt. % low density polyethylene; or about 60 wt. % calcium carbonate, about 20 wt. % linear low density polyethylene, about 10 wt. % high density polyethylene and about 3 wt. % low density polyethylene.
In the structure, the outer layer can be comprised of low density polyethylene, the bulk layer can be comprised of polyethylene and from about 30 to about 75 percent by weight calcium carbonate based on the weight of the bulk layer, and the inner layer can be comprised of a blend of low density polyethylene and linear low density polyethylene. In the structure, the outer layer can be comprised of low density polyethylene, the bulk layer can be comprised of about 52.5 wt. % calcium carbonate, about 17.5 wt. % linear low density polyethylene, about 20 wt. % high density polyethylene and about 3 wt. % low density polyethylene, and the inner layer can be comprised of a blend of low density polyethylene and linear low density polyethylene.
This invention is also directed to a collapsible dispensing container having a body wall that is formed of an asymmetric multilayer plastic structure having a barrier layer, adhesive layers, inner and outer surface layers, and a bulk layer as described above wherein the calcium carbonate is present in an amount sufficient that the body wall has improved product dispense properties as compared with a multilayer plastic dispensing container that does not have calcium carbonate in a layer of its body wall. The barrier layer can comprise an ethylene vinyl alcohol copolymer, a polyamide or a polyester.
This invention is additionally directed to a method of forming a six-layer asymmetric plastic structure that has a barrier layer of ethylene vinyl alcohol copolymer and has an acceptable level of curling, which comprises coextruding the six-layer structure whose layers consist of the barrier layer, an adhesive layer on each surface of the barrier layer, inner and outer surface layers, and a bulk layer positioned between one of the surface layers and an adjacent one of said adhesive layers, the bulk layer being comprised of a thermoplastic polymer and calcium carbonate in an amount of from about 30 to about 75 percent by weight based on the weight of the bulk layer. The method can include the step of providing that the calcium carbonate comprises about 60 wt. % to about 70 wt. % of the bulk layer and contains less than 200 ppm moisture.